crap seems much faster with Ready Boost - I have Vista Basic and a gig of memory on a 1.7 ghz laptop with a 5000 something rpm hd. I use open office on this thing and it usually takes a little while to open - much faster now. Maybe it is a placebo effect, but it sure does seem faster to me.
When you insert a Flash Drive Vista speed tests, and then if the stick is fast enough it will offer to "Speed up Windows". If you click yes it pops up a slider that asks how much memory you want to use. I chose all of it myself. Apply, and there you are. Not sure if it will keep asking you if you keep the stick there. Might be interesting on desktop systems - plug, set, and forget.
I did read that Ready Boost can only handle a 4 gig drive or lower, and not all drives will work (has to be fast enough).
I will definately experiment some more later.